Technical Field
The present disclosure generally relates to helicopters, and more specifically to anti-torque devices that alter the aerodynamics of a helicopter.
Description of the Related Art
Traditional single rotor helicopters have a main lifting rotor (“main rotor”) that provides a lifting force and a tail rotor that provides a laterally directed force used to counter reaction torque of the main rotor and adjust yaw alignment. The main rotor generates downwash that flows around the tail boom of the helicopter. It is known to include strakes on the approaching side of the tail boom to alter the flow of downwash from the rotating main rotor so as to generate a compensation force that at least partially counteracts the reaction torque produced by rotation of the main rotor. The “approaching side” of the tail boom is the side of the tail boom the main rotor blade approaches during rotation.
For example, U.S. Pat. No. 4,708,305 describes a system for controlling main rotor torque which reduces the power and size requirements of conventional anti-torque means (such as a tail rotor). Torque countering forces are generated by disrupting the main rotor downwash flowing around the fuselage. In particular, the downward flow is separated from the fuselage surface by strakes positioned at specified locations on the approaching side of the tail boom.
U.S. Pat. No. 8,210,468 describes a stabilizer system for a helicopter that includes strakes installed on the approaching side of the tail boom and a modified vertical stabilizer. The components of the stabilizer system cooperate to improve handling of the helicopter (e.g., increased cross wind tolerance), reduce fatigue (e.g., tail boom fatigue, fuselage fatigue, and the like), improve climb performance, improve cruise performance, increase control safety margins, combinations thereof, and the like.
U.S. Pat. No. 8,985,503 teaches locating strakes at two positions on the approaching side of the tail boom. A lower strake extends generally downward from a location of flow separation or maximum change in a curvature of an outer surface on a lower half of the tail boom. An upper strake extends generally upward from a location of maximum change in a curvature of the outer surface on an upper half of the tail boom. U.S. Pat. No. 8,985,503 also teaches inclusion of a fairing on a retreating side of the tail boom. The retreating side is the side of the tail boom that the main rotor retreats or moves away from during rotation. The fairing is located on the upper half of the tail boom. U.S. Pat. No. 8,985,503 further teaches locating a number of vortex generators on the retreating side of the tail boom. The vortex generators are positioned on the fairing, thus extending along a portion of the upper half of the tail boom. U.S. Pat. No. 8,991,747 teaches structures that are similar in some respects to those taught in U.S. Pat. No. 8,985,503.